As integrated circuits have become smaller, the demands to achieve submicron resolution with sufficient line width control on a substrate have become increasingly important. This in turn has led to problems in patterning integrated circuit workpiece surfaces with extreme topography by means of a single photoresist layer.
To meet this problem, bilayer and trilayer photoresist systems have been developed. Standard multilayer lithographic techniques, however, have problems in throughput rates, complications of processing, uniformity control, cleanliness, layer cracking and removal of deposited layers. Additionally, although the multilayer systems prove adequate for building test designs at small geometries, their introduction into the production line is not very likely due to the high complexity of the processes.
More recently, single-layer and multi-layer photoresist technologies have been developed which obtain more desirable characteristics than the older multilayered systems. One example of these technologies is a photoresist process called DESIRE, an acronym for diffusion-enhanced silylating resist. Silylation is a process whereby silicon is incorporated into a polymer by exposing the material to a gaseous or liquid silicon-bearing compound such as hexamethyldisilazane (HMDS). The DESIRE process has been found to be highly selective in transforming a latent optical image into a latent "silicon" image. The silicon image is subsequently used to produce a relief image by dry-etching in oxygen. L, F. Coopmans et al., "DESIRE: A New Route to Submicron Optical Lithography", Solid State Technology, June, 1987.
Typically, oxygen is used as a reagent to dry etch/dry develop multi-layer and new single-layer, surface-imaging resists. The use of oxygen has several drawbacks. First, the relatively heavy oxygen ions, such as O.sub.2 +, sputter underlying material (especially metal) onto the photoresist sidewalls. Second, the sputtered material becomes oxidized, making it more difficult to remove in situ. Third, ion bombardment by high-mass O.sub.2 + may cause damage to the substrate and to the mask, reducing definition. This results in reduced yields.
A need has therefore arisen for an improved photolithographic dry-develop process which does not have the unwanted side effects of using conventional oxygen reagents to develop the photoresist.